As Netflix Grows, Profit Remains Small

Stock Soars as Video Service Adds Subscribers

Netflix Inc. added 1.3 million U.S. customers in the third quarter, continuing on a pace to surpass Time Warner Inc.'s HBO in paying viewers—even as questions remain about the streaming video provider's profit-growth potential.

Netflix ended the quarter with 29.93 million paid domestic users. HBO—which Netflix has sought to emulate with original programming—had 28.96 million U.S. subscribers as of June 30, the latest data available,...